Field of the Invention
The present invention relates to a system and a method for estimating the change in the posture of the upper body of a person (subject).
Description of the Related Art
Hitherto, in order to grasp the walking state of a person, the posture of a predetermined part of a walking person, or a change or the like of the posture has generally been measured using an angular velocity sensor, such as a gyro sensor.
For example, Japanese Patent Application Laid-Open No. 2012-65723 (hereinafter referred to as Patent Document 1) describes a technique in which gyro sensors are attached to the waist and the thigh, the crus and the foot of each leg of a walker, and the joint angles of a hip joint, a knee joint, and an ankle joint are measured using the detection values of the gyro sensors.
In the meantime, according to various experiments and studies carried out by the inventors of the present application, the change in the posture of the upper body of a walking person, especially the change in the posture of the upper body in a pitch direction or a roll direction is markedly influenced by the motions of the legs of the walking person.
Further, especially the angular acceleration of the upper body is closely connected with the state of a floor reaction force acting on the walking person.
Therefore, observing the change in the posture of the upper body, including the angular acceleration, of the upper body of the walking person is highly necessary for grasping or assessing the walking state (e.g. the motional balance of right and left legs or the state of a leg motion recovered by rehabilitation) of a person.
In this case, angular velocity sensors, such as gyro sensors, could be attached to the upper body of a person, so that the change in the posture of the upper body could be observed based on the detection values of the angular velocities indicated by the angular velocity sensors. Further, in this case, as with the gyro sensor on the waist described in Patent Document 1, an angular velocity sensor could be attached to the upper body of a person through a fixing plate, such as a wide belt.
However, according to the technique in which an angular velocity sensor is attached to the upper body of a person through a fixing plate, such as a wide belt, as described above, the fixing plate is placed on a relatively large contact surface of the upper body of a person. This tends to cause the person discomfort or the feeling of an attached foreign object.
Further, in some cases, the discomfort, the feeling of an attached foreign object or the weight of the fixing plate inconveniently causes the walking form of a person to be different from his/her normal walking form without the fixing plate attached. This makes it impossible to properly assess the walking state of the person with high reliability.
To avoid the aforesaid inconvenience, the contact area occupied by the angular velocity sensor attached to the upper body of the person could be minimized.
This, however, would make it difficult to cause the attitude of the angular velocity sensor to accurately and stably follow the posture of the upper body of the person. Hence, the change in the attitude of the angular velocity sensor tends to deviate from the actual change in the posture of the upper body. As a result, it becomes difficult to observe the posture change of the upper body of the person with high reliability.
Further, if, for example, the angular acceleration of the upper body of a person is to be measured using an angular velocity sensor attached to the upper body, then it is necessary to carry out calculation for differentiating the detection values of the angular velocity obtained by the angular velocity sensor. Therefore, the measurement values of the angular velocity of the upper body are susceptible to the influence of noise components contained in the detection values of the angular velocity. This is inconveniently prone to result in deteriorated measurement accuracy of the angular acceleration of the upper body.